This invention relates generally to solenoid actuated valves, and more particularly, to solenoid actuated valves including an external sleeve armature.
Spool valves are commonly used for controlling the delivery of fluid, particularly in applications requiring a relatively fast operating time. Spool valves are solenoid operated valves which include a valve spool located within a valve body and movable relative to the valve body between fluid flow permitting and fluid flow preventing positions. The valve spool determines flow paths and as such dictates the size of the valve ports. Because the valve spool is located within the valve body, the outer diameter of the valve spool has to be smaller than the inner diameter of the valve body.
Many fluid flow control applications require rapid shifting movement of the valve spool. One factor in determining the operating time of a direct acting solenoid operated valve is the magnetic force produced by the solenoid. Because the magnetic force is proportional to the cross-sectional areas of coextensive portions of the valve spool and the pole member, when the valve spool is small in size, the magnetic force is also small with the spool acting as an armature. Another factor in determining the operating time of a solenoid operated valve is the mass of the movable valve member, such as a valve spool. The larger the mass of the valve spool, the greater the magnetic force must be to accelerate the valve spool in the desired direction.
One application of spool valves is in the field of inflatable safety restraints for occupants of a vehicle for reducing the possibility of injury to such occupants during a crash. Typical inflatable restraint systems include an inflatable restraint, a source of pressurized gas, and a control mechanism. The control mechanism couples the inflatable restraint to the source of pressurized gas to rapidly inflate the inflatable restraint with the pressurized gas if the vehicle is subjected to a high rate of acceleration or deceleration, as may be caused by a crash, for example.
Many inflatable restraint systems use mechanical or pyrotechnic systems to control inflation of the inflatable restraint. This is partly attributable to the relatively slow response time of known electronically controlled valves. In some valves, mechanical springs are used to bias the valve to its closed position. The force of the spring bias must be overcome to allow the valve to be operated to its open condition. However, the use of spring bias increases the response time for the valve. In addition, the use of a bias spring to move the valve member to one of its positions results in less control, particularly when a shuttling type of operation is desired.
Moreover, the use of a conventional spool valve in inflatable restraint systems can be detrimental because of the small size of the valve spool. In applications such as inflatable restraint systems, particulate matter flows through the valve during operation. The spool bore inlets or outlets can become clogged with the particulate matter during operation of the valve, affecting the distribution pattern for the high pressure fluid being supplied to the inflatable restraint by the valve.